1. Field of the Invention
The present invention relates to a double cycle internal combustion engine whose combustion operation can be switched from two cycle mode to four cycle mode or vice versa as occasion demands.
2. Description of the Prior Art
Internal combustion engines of a reciprocation type can be classified into two cycle engines and four cycle engines from the structural standpoint. In the two cycle engine, since fuel is burnt once for each piston reciprocation, the number of explosions is large and therefore there exists such an advantage that a high power can be outputted in spite of a small size. However, there exists a problem in that the fuel consumption rate is not low, because it is rather difficult to effect perfect scavenging and exhausting operations. An example of these two cycle engines is disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 63-32256.
In contrast with this, in the case of the four cycle engine, since fuel is burnt once every two piston reciprocations, reliable suction and exhaustion operations can be effected and therefore fuel can be burnt perfectly so that the fuel consumption rate is low. However, there exists another problem in that the four cycle engine is inferior to the two cycle engine with respect to high speed revolution and high output power.
To overcome the above-mentioned problems, there has been proposed an engine whose combustion operation can be switched to the four cycle mode when the engine is being operated under a relatively low load (partial load operation) to improve the fuel consumption rate, and to the two cycle mode when the engine is being operated under a relatively high load (full load operation) to obtain a high output power.
In the above-mentioned prior-art two and four cycle switchable internal combustion engine, however, there exists a problem in that the mechanism or the structure for switching the operation modes is very complicated and therefore large in scale.
In the case of the engine as disclosed in the above-mentioned application (JP-58-152139), for instance, since the operation modes are switched by switching the operating timing of the suction and exhaust valves, a two cycle cam and a four cycle cam are both attached to a cam shaft and these two cams are switched by sliding the cam shaft in the axial direction thereof, so that the structure of the operating valves are complicated markedly.